1. Field of the Invention
The present invention relates to a set-up/down weir made of a flexible sheet, and particularly relates to a set-up/down plural-span weir assembly made of flexible sheets and improved in set-down means based on the level of water upstream of the weir assembly.
2. Description of the Prior Art
A weir made of a flexible sheet such as a rubberized cloth and capable of being set up and down is provided with a bag made of the flexible sheet and mounted on at least the bed of a river or the like across the stream thereof, as disclosed in the Japanese Patent Publication Nos. 11702/65 and 2371/69. A pressure medium such as air, water, both of them or the like is introduced into the bag to inflate it to set up the weir. The pressure medium in the bag is discharged therefrom to deflate it to set down the weir.
A plurality of such single-span weirs can be installed in a river of large width across the stream thereof to facilitate the regulation of the level or flow rat of water, the removal of deposited earth and sand, the shut-off of the river or the like. In that case, the single-span weirs are coupled to each other through pillars so that a set-up/down plural-span weir assembly is constituted. The number of the single-span weirs to be thus coupled is not single, but may be two, three or more.
The single-span weirs of a conventional set-up/down plural-span weir assembly of such kind are provided with set-down means which do not act in conjunction with each other but act separately from each other, as shown in FIGS. 6 and 7, so that the single-span weirs are set down by the set-down means when the upstream water of the weir assembly has reached prescribed levels, respectively.
The set-down means of such a conventional set-up/down plural-span weir assembly shown in FIG. 6 are of a bucket type. When the upstream water W of the weir assembly has reached an automatic set-down level L.sub.1, the upstream water W flows into buckets 11a and 11c to move down the buckets to open butterfly valves 8a and 8c thereby to deflate the bags 1a and 1c of the single-span weirs of the assembly. As a result, the single-span weirs are set down. When the up-stream water W has reached another automatic set-down level L.sub.2, the upstream water W flows into another bucket 11b to move down the bucket to open another butterfly valve 8b therby to deflate the bag 1b of the other single-span weir of the assembly. As a result, the other single-span weir is set down.
The set-down means of such a conventional set-up/down plural-span weir assembly shown in FIG. 7 are of a float type. When the upstream water W of the weir assembly has reached an automatic set-down level L.sub.1, the upstream water flows into float containers 21a, 21b and 21c to lift floats 24a, 24b and 24c to the same level to open butterfly valves 8a and 8c by rods 22a and 22c coupled to the floats 22a and 24c, therby to deflate the bags 1a and 1c of the single-span weirs of the assembly. As a result, the single-span weirs are set down. When the upstream water W has reached another automatic set-down level L.sub.2, the float 4b is lifted further to open a butterfly valve 8a by a rod 22b coupled to the float, to deflate the bag 1b of the other single-span weir of the assembly. As a result, the other single-span weir is set down.
As understood from the above description, the single-span weirs of each of the conventional plural-span weir assemblies cannot be set down in prescribed order without presetting a plurality of different set-down levels for the upstream water. However, it is desired for the following reasons (1) and (2) that the single-span weirs can be set down in prescribed order (for example, each of the single-span weirs or every plurality of them can be sequentially set down) without presetting a plurality of different set-down levels for the upstream water.
(1) As for the discharge of stored water at the time of low level of the upstream water or at the slow gradient of the river or the like, it takes much time to store enough water upstream of the weir assembly set up again after being set down completely. In that case, it is not easy to obtain enough water shortly. For that reason, each of the single-span weirs of the assembly or every plurality of the single-span weirs, for example, should be sequentially set down according to the rate of increase of the upstream water so that the discharged quantity of stored water upstream of the weir assembly is reduced as much as possible.
(2) It is preferable that water can be always obtained from the weir assembly for electricity generation, tape water supply or the like. For that reason, the upstream water of the weir assembly should be maintained on a prescribed level or above it. If the upstream water is to be discharged downstream, the single-span weirs of the assembly should not be all set down simultaneously but each of the single-span weirs or every plurality of them, for example, should be sequentially set down according to the rate of increase of the upstream water to keep the level of the upstream water as high as possible.